Processes for removal of lactose from dried milk products

ABSTRACT

Disclosed are processes for removing lactose from dried milk products to produce dried protein fortified and/or mineral fortified milk products having a reduced lactose content with minimal use, or even without the use, of membrane ultrafiltration, diafiltration, or additional drying equipment. Additionally, a high lactose-containing stream product is also produced. The dried protein fortified milk products are physically and chemically similar to dried milk protein concentrates and can be used for protein fortifiers in various food applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Ser. No. 61/599,207, filed Feb. 15, 2012, which is hereinincorporated by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

The present disclosure generally relates to processes for removinglactose from dried milk products. More particularly, the presentdisclosure is directed to processes for removing lactose from dried milkproducts, and in particular, skim milk powder, to produce dried proteinfortified and mineral fortified milk products having reduced lactose.The present disclosure is additionally directed to dried proteinfortified milk products with reduced lactose content prepared usingthese processes.

Skim milk powders, which provide a method of storing and moving surplusskim milk, have conventionally been used by food manufactures forprotein fortification of formulated food products. The protein fractionof skim milk powder, which accounts for approximately 36% by weight ofthe powder, contains caseins and whey proteins in about a 5:1 ratio,respectively. The use of skim milk powders in many of these foodapplications is limited, however, as the powders include a high lactosecontent, accounting for approximately 51% to 56% by weight of thepowder, which can potentially jeopardize the quality of the final foodproduct through lactose crystallization.

More particularly, the chemical composition of concentrated skim milkprior to spray drying is well beyond the lactose supersaturation point,thus favoring lactose crystallization. Due to the kinetics of thereaction, however, the appearance of the crystals at disenable size isnot common during production of skim milk powder. This is attributed tothe slow rate of nucleation of the crystals and the conditions typicallyemployed in the production of dried skim milk that disfavor crystalgrowth. If the concentrated skim milk is held for some time at lowertemperatures before spray drying, however, lactose will eventuallycrystallize.

Previous attempts to overcome the above shortcomings have includedturning to the use of dried milk protein concentrates having reducedlactose and mineral contents. The casein and whey protein ratio in milkprotein concentrate is typically similar to skim milk powder, allowingthe milk protein concentrate to have the same, or similar, functionalproperties as skim milk powder with reduced potential for lactosecrystallization.

Manufacturing processes of milk protein concentrates are similar to skimmilk powder with the use of concentrating and drying technologiesintended to extract water from the skim milk. However, additionalprocessing steps such as ultrafiltration (UF) are required prior toevaporation for the reduction of lactose, minerals, small molecules, andwater. The UF membrane is designed with small pores that allow lowmolecular weight components (i.e., permeate) to pass through while largemolecules (i.e., retentate) are prevented to pass though. As the UF isbeing applied, the skim milk solids concentration (i.e., retentate)increases, thereby increasing viscosity, to a point where the flux ofcomponents through the membrane will be reduced. The maximum level ofconcentration for the retentate is dependent upon membrane fouling andproduct viscosity, consequently affecting the efficiency of the process.At this point, the UF processing may be stopped and evaporation methodsare employed to remove water, further concentrating the solids of theskim milk. Additional processing using UF may be done with the additionof water (i.e., diafiltration (DF)) to reestablish the flux and removemore lactose and minerals.

Inherent limitations of UF include fouling of the UF membrane. Further,UF membrane installations are capital intensive, require significantoperating expense (i.e., cleaning and sanitation chemicals), increasedwater use, increased wastewater, and use excessive energy.

Accordingly, there is a need in the art to develop alternative processesfor producing dried protein fortified milk products having similarprotein concentrations as dried milk protein concentrates and skim milkpowder, while having reduced lactose levels. Particularly, it would beadvantageous to develop processes of producing the dried proteinfortified milk products that require less or no membrane processing,less energy, and less water usage and wastewater.

SUMMARY OF THE DISCLOSURE

The present disclosure is generally directed to processes for removinglactose from dried milk products to produce dried protein fortified milkproducts having reduced lactose content. The dried protein fortifiedmilk products can be used as alternatives to skim milk powder and driedmilk protein concentrates as protein fortifiers for use in formulatedfood products.

In one aspect, the present disclosure is directed to a process forpreparing a dried protein fortified milk product having reduced lactosecontent. The process comprises: reconstituting skim milk powder withwater to produce a solution with about 40% solids by weight;pasteurizing the solution; cooling the pasteurized solution;crystallizing lactose in the cooled solution; spray drying the solutioncomprising the lactose crystals to produce a dried milk product; andseparating the lactose crystals from the dried milk product to producethe dried protein fortified milk product.

In another aspect, the present disclosure is directed to a process forpreparing a dried protein fortified milk product having reduced lactosecontent. The process comprises: pasteurizing a liquid skim milk solutionhaving a solids content of about 40% by weight; cooling the pasteurizedsolution; crystallizing lactose in the solution; spray drying thesolution comprising the lactose crystals to produce a dried milkproduct; and separating the lactose crystals from the dried milk productto form the dried protein fortified milk product.

In still another aspect, the present disclosure is directed to a driedprotein fortified milk product having reduced lactose content. The driedprotein fortified milk product is prepared by a process comprising:pasteurizing a skim milk solution having a solids content of about 40%by weight; cooling the pasteurized solution; crystallizing lactose inthe solution; spray drying the solution comprising the lactose crystalsto produce the dried milk product; and separating the lactose crystalsfrom the dried milk product to form the dried protein fortified milkproduct.

It has been found that lactose can be removed from dried milk productsto produce dried protein fortified milk products having a reducedlactose content with minimal use, or even without the use, of membraneultrafiltration, diafiltration, or additional drying equipment. Theseproduction processes save energy, as measured per unit of proteinconcentration, as well as reduce the energy-related environmentalimpact, as compared to conventional milk protein concentrate productionprocesses. Additionally, these processes reduce water use and theenvironmental impact of wastewater effluent, as measured per unit ofprotein concentration, as compared to conventional milk proteinconcentration production processes.

Moreover, the processes of the present disclosure may produce a driedprotein fortified milk product with Class I (superior) nutrientretention and Third Group (inferior) nutrient reduction such that thedried protein fortified milk products could be labeled“Protein-Fortified Skim Milk Powder” as allowed by the Food and DrugAdministration. This label could be used in standardized foods and couldthus enhance “clean label” positioning of milk-based and otherformulated food products.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be better understood, and features, aspects andadvantages other than those set forth above will become apparent whenconsideration is given to the following detailed description thereof.Such detailed description makes reference to the following drawings,wherein:

FIG. 1 depicts a flow diagram of one particular process disclosed in thepresent disclosure.

FIG. 2 depicts the α-monohydrate and β-anhydrate forms of lactose.

FIGS. 3A and 3B depict exemplary U-shaped agitators for use in theprocesses of the present disclosure.

FIG. 4A depicts particle size distribution prior to air classificationof Control Sample as analyzed in Example 2.

FIG. 4B depicts particle size distribution prior to air classificationof Test Sample as analyzed in Example 2.

FIG. 5A depicts particle size distribution of fine stream post airclassification of Control Sample as analyzed in Example 2.

FIG. 5B depicts particle size distribution of coarse stream post airclassification of Control Sample as analyzed in Example 2.

FIG. 5C depicts chemical analysis of Control Sample prior to and postair classification as analyzed in Example 2.

FIG. 5D depicts particle size distribution of fine stream post airclassification of Test Sample as analyzed in Example 2.

FIG. 5E depicts particle size distribution of coarse stream post airclassification of Test Sample as analyzed in Example 2.

FIG. 5F depicts chemical analysis of Test Sample prior to and post airclassification as analyzed in Example 2.

FIG. 6 depicts a lactose supersolubility diagram as used in Example 3.

FIG. 7 depicts the applied crystallization cooling rates as analyzed inExample 3.

FIG. 8A depicts lactose crystals in concentrated skim milk after 24 hourcrystallization as analyzed in Example 3.

FIG. 8B depicts lactose crystals in concentrated skim milk after 48 hourcrystallization as analyzed in Example 3.

FIG. 9 depicts a chart of standardized effects on 24 hourcrystallization response of lactose as analyzed in Example 3.

FIG. 10 depicts a chart of standardized effects on 48 hourcrystallization response of lactose as analyzed in Example 3.

FIG. 11 depicts particle size distribution for coarse stream test sampleand fine stream test sample as analyzed in Example 4.

FIG. 12 depicts box plots of mean crystal size of lactose crystalsformed and analyzed from skim milk concentrate in Example 5.

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described below in detail. Itshould be understood, however, that the description of specificembodiments is not intended to limit the disclosure to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the disclosure as defined by the appended claims.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the disclosure belongs. Although any processes andmaterials similar to or equivalent to those described herein may be usedin the practice or testing of the present disclosure, suitable processesand materials are described below.

As used herein, the term “feed stock” refers to any raw dairy or milkcomponent for use in a large scale industrial process. Exemplary feedstocks for use in the methods of the present disclosure include wholemilk, skim milk, whey, and whey permeate.

In accordance with the present disclosure, it has now been estimatedthat dried protein fortified milk products can be prepared havingsimilar chemical and physical characteristics as milk proteinconcentrates without the use of membrane ultrafiltration, diafiltration,or additional drying equipment, thus, saving production costs, energy,and reducing environmental impact. Particularly, these processes reducewater use and the environmental impact of wastewater effluent, asmeasured per unit of protein concentration, as compared to conventionalmilk protein concentration production processes.

It should be understood that while discussed herein as removing lactosefrom dried milk products to produce dried protein fortified milkproducts, the processes described may also be used to produce a milkproduct having increased concentrations of other dairy components (e.g.,minerals). More particularly, by removing the lactose through the use ofair classifiers as described herein, fortified dairy products havinghigher concentrations of various dairy components may be prepared. Thesefortified protein products and other fortified dairy products canultimately be used as feed stock.

Processes for Removal of Lactose

In one aspect, the present disclosure is directed to processes forremoving lactose from dried milk products to produce dried proteinfortified milk products having reduced lactose content. The processes ofthe present disclosure provide dried protein fortified milk productshaving similar characteristics, including protein content and lactosecontent, to dried milk protein concentrates, with minimal to no use ofmembrane filtration, thereby reducing energy expense, water use, andwastewater.

Additionally, the processes produce a second high lactose-containingproduct (also referred to herein as the “coarse stream”). This coarsestream may be used in foods, beverages and like nutritional applicationsas a lactose fortification product.

Generally, the processes of the present disclosure include: pasteurizinga skim milk solution having a solids content of about 40% by weight;cooling the pasteurized solution; crystallizing lactose in the solution;spray drying the solution comprising the lactose crystals to produce thedried milk product; and separating the lactose crystals from the driedmilk product to form the dried protein fortified milk product. Oneparticularly suitable process for use in the present disclosure isdepicted in the flow diagram of FIG. 1.

A skim milk solution may be obtained from any suitable source known toone skilled in the art. In one embodiment, the solution is obtained byreconstituting a skim milk powder with water. When reconstituting a skimmilk powder, it is suitable to hydrate the powder for a period of fromabout 12 hours to about 24 hours or more under refrigeration conditions.As used herein, the term “refrigeration conditions” refers to processingunder temperatures in the range of from about 0° C. to about 7° C., andincluding from about 4° C. to about 7° C. This hydration period ensuresthe full hydration of the powdered milk; including reversal of thepowder to the original milk protein and water interaction to ensure goodmouthfeel of the final dried protein fortified milk product. In anotherembodiment, the process begins with a commercially available liquid skimmilk solution having a solids content of about 40% by weight.

Once a skim milk solution is obtained, the solution is pasteurized. Thismethod of heat treatment intends to inactivate any pathogenicmicroorganism and inhibit as many enzymes as possible. Pasteurization ofmilk products typically uses a combination of time-temperatureconditions that mandates the intensity of the heat treatment. Thesetime-temperature conditions are typically established based oninactivation of Coxiella burnetti, the most thermal resistant non-sporeformer currently recognized in the art (its inactivation takes place atapproximately 63° C. for 30 minutes, 72° C. for 15 seconds, or 65° C.for 2 minutes). Typically, the solution is pasteurized using anysuitable pasteurization method known to one skilled in the art,including, for example, low-temperature-long-time (LTLT) pasteurization,high-temperature-short-time (HTST) pasteurization, ultra pasteurization,and ultra heat treatment (UHT). Pasteurization, which may vary in timeand temperature, is conducted at minimum time and temperature ranges toensure bacterial heat deactivation. Without being limiting, suitablepasteurization times and temperatures for various milk solutions areshown in the Table below. It should be understood that all amounts arepreceded by the term “about”.

TABLE Summary of the Most Common Commercial Pasteurization MethodsPasteurization Method Temperature, ° C. Holding Time LTLT for milk 63 30minutes LTLT for products with more than 66 30 minutes 18% (w/w) totalsolids HTST for milk 72 15 seconds HTST for products with more than 7420 seconds 18% (w/w) total solids High pasteurization 85 20 secondsUltra pasteurization 138   4 seconds UHT 135-150  5 seconds

Suitably, in one aspect, the skim milk solution is pasteurized at atemperature of from 66° C. to about 150° C. for a period of from about 5seconds to about 30 minutes. In one particular embodiment, the skim milksolution is pasteurized at a temperature of about 71° C. for a period ofabout 30 minutes.

In one aspect, the skim milk solution is tempered at room temperaturefor a period to activate any non-vegetative bacteria or spores presentin the solution prior to pasteurization. For example, in one particularembodiment, the skim milk solution is tempered at room temperature forfour hours to allow for activation of these microorganisms.

The processes of the present disclosure further include cooling thepasteurized solution. Suitably, the pasteurized solution is cooled to atemperature of 12° C. or less to allow for crystallization of thelactose in the solution and/or to condition the solution for seedingwith lactose crystals. This initial cooling is typically conducted bysubmerging the pasteurized solution in thermostatically controlledchilled water to ensure the solution cools to a temperature of 12° C. orless. The cooling period typically will depend upon the size of thesample.

Lactose crystallization consists in the self arrangement of moleculeswith a regular pattern into a lattice structure. Prior tocrystallization, lactose has to meet the following criteria: generationof a supersaturation state, nucleation (i.e., formation of crystallinelattice structure from solution or melt), growth, and recrystallization.Lactose can crystallize in two crystalline forms or as a non-crystallineamorphous glass. Amorphous lactose results from rapid evaporation ordrying processes, wherein crystalline lactose such as α-monohydrate and3-anhydrate lactose results from slow crystallization with a temperatureof less than 93.5° C. for α-monohydrate and greater than 93.5° C. forβ-anhydrate. β-anhydrate lactose typically crystallizes in anuneven-sided diamond, whereas α-monohydrate typically crystallizes in atomahawk shape (see FIG. 2). The crystallization rate, temperature, pH,viscosity, and presence of impurities (e.g., riboflavin, calcium, traceelements, salts (e.g., sodium, potassium, calcium, magnesium, chloride,phosphorus, iron, zinc, copper, manganese, and selenium salts)) in theskim milk solution can alter the shape of the crystals. By controllingthe size and shape of the lactose crystals formed, and particularly, bycontrolling the rate of crystallization, tomahawk crystals ofα-monohydrate lactose are obtained, which can provide advantages forcertain food applications and processes such as improved shelf life asthe tomahawk crystals, including a molecule of water, will not absorbwater from atmospheric moisture.

In accordance with the above, once the pasteurized solution has beencooled to 12° C. or less, it may be suitable to further cool thepasteurized solution at a controlled cooling rate to further control thesize and shape of lactose crystals formed. Suitably, the pasteurizedsolution is further cooled to a temperature of from about 5° C. to about10° C. to allow for lactose crystallization. It is particularly suitableto further cool the cooled solution at a cooling rate of from about 0.2°C. to about 0.4° C. per hour continuously over a period of from about 12hours to about 48 hours, and including from about 24 hours to about 48hours, to allow for controlled crystallization of lactose in the cooledsolution.

In one aspect, the cooled solution is agitated during cooling using anyagitator as suitably known in the art. By way of example, the solutioncan be agitated using a U-shaped agitator (FIGS. 2A and 2B) at a speedof from about 50 rpm (approximately 5.24 radian/second) to about 100 rpm(approximately 10.47 radian/second) with an agitator angular speed ofabout 9 rpm (approximately 0.94 radian/second) and about 17 rpm(approximately 1.78 radian/second). Agitation during cooling promotesheat transfer within the colloidal suspension. As crystallization is anexothermic reaction, agitation aids in transferring the heat from theinterior of the reactor to its outer walls. Heat will then be dissipatedwith the cold temperature such as from the thermostatically controlledchilled water used for cooling as described above.

As noted above, lactose generally crystallizes from solutions dependingon concentration and temperature; however, lactose crystallization maynot be immediate due to the slow rate of reaction, even undersupersaturated conditions. Increasing the lactose concentration ordecreasing the temperature of the solution, as described above, or bothcan enhance this reaction. Additionally, the rate of crystallization oflactose can also be increased with the addition of preformed lactosecrystals (i.e., seeds). The addition of crystals, referred to asseeding, provide nucleation points that counteract the otherwise slownucleation of lactose crystals from concentrated solutions. Preformedlactose crystals can be obtained from prior production batches or arecommercially available from suppliers such as Leprino Foods (Denver,Colo.). Typically, the lactose crystals used in seeding the cooledsolution are sized from about 40 mesh to about 200 mesh.

In one suitable aspect, the process includes seeding the cooled solutionthrough the addition of from about 0.005% by weight to about 0.010% byweight lactose crystals to the cooled solution. These low seedingconcentrations help to achieve the growth of large lactose crystals.

As described above, the lactose crystals formed through crystallizationwill vary in size and shape depending on the degree of supersaturation,temperature of crystallization, and concentration of impurities (e.g.,minerals and riboflavin) in the solution. Typically, however, thelactose crystals formed in the present processes are α-monohydratetomahawk-shaped crystals having a size of approximately 93 μm±46 μm.

Once lactose crystals have formed in the solution, the solution is spraydried to form a dried milk product. Typically, the solution is spraydried to produce a dried milk product having a moisture content of lessthan 5% by weight, and including from about 2.5% by weight to about 4%by weight moisture.

Any means for spray drying known in the art can be used in the processesof the present disclosure to dry the solution. In one aspect, thesolution is spray dried at a temperature of from about 150° C. to about220° C. By way of example, the solution may be spray dried in a dryerhaving an inlet air temperature of from about 150° C. to about 220° C.and an exhaust temperature of from about 85° C. to about 100° C. Theresulting dried milk product typically has a temperature of from about40° C. to about 60° C. when leaving the spray dryer.

Once dried, the lactose crystals are separated from the dried milkproduct. While the lactose crystals may be separated using any sievingmethod known in the art, including for example, fine mesh screening andcyclonic separators, it has been found that one significantly moreefficient separation method includes an air classifier.

In one exemplary embodiment, the classification process initiates when afeed stock material of the dried product is directly and continuouslyfed into the classifier. The feed stock material is introduced into theclassifying chamber through a conduit on the top of the classifier. Asthe feed stock material enters the chamber, the material is mixed withupwardly moving air generated from external blowers and introduced tothe system through an annular conduit equipped with screens and baffles.The upright air flow promotes the separation of coarse and fineparticles by dropping the coarse particles to the bottom of the chamber.Fine particles are aerodynamically dragged into a discharge conduit anddelivered to a cyclone that separates the air and fine stream.Accordingly, in one particularly suitably aspect, the lactose crystalsare separated using an air classifier, for example, the TurboClassifier, commercially available from Nisshin Engineering Inc. (Tokyo,Japan). Another suitable commercially available air classifier includesan air classifier from RSG, Inc. (Sylacauga, Ala.).

It should be understood by one skilled in the art that while discussedas a singular separation process, the lactose crystals may be separatedusing a series of separation processes. For example, in one desiredembodiment, the lactose crystals are separated using a process of airclassifiers in series. In another embodiment, the lactose crystals areseparated by running the dried milk product through a separator (e.g.,air classifier) multiple times.

By separating the lactose crystals, a dried protein fortified milkproduct having a reduced lactose content is produced. This product, alsoreferred to herein as the fine stream, includes proteins andnon-crystallized lactose, among other small components, having a size offrom about 20 μm to about 50 μm. Also produced is a high lactosecontaining coarse stream including the larger lactose crystals removedfrom the dried protein fortified milk product.

It should be understood by one skilled in the art that parameters usedin the processing conditions described herein can adjusted such as toadjust flow rate through processing equipment, size of lactose crystalsformed and removed from the fine stream, and the like.

Dried Protein Fortified Milk Products

In another aspect, the present disclosure is directed to a dried proteinfortified milk product having a reduced lactose content prepared usingthe above-described processes. The dried protein fortified milk productis estimated to have similar chemical and physical properties toconventional dried milk protein concentrates. Desirably, the driedprotein fortified milk product has a protein content of from about 38%by weight to about 56% by weight. In some particularly desiredembodiments, the dried protein fortified milk product has a proteincontent of from about 38% to about 44%, and including from about 38% toabout 42% by weight. In other embodiments, the dried protein fortifiedmilk product has a protein content of from about 40% to about 56%,including from about 44% to about 56%, and even including from about 45%to about 52% by weight. Additionally, the dried protein fortified milkproduct typically has a ratio of casein:whey of approximately 5:1,similar to conventional milk protein concentrates.

Further, the dried protein fortified milk products prepared using theabove-described processes have a reduced lactose content similar to milkprotein concentrates, including an estimated lactose content of fromabout 35% by weight to about 56% by weight, including from about 35% byweight to about 52% by weight, including from about 35% by weight toabout 46% by weight, and including from about 40% by weight to about 45%by weight lactose.

The dried protein fortified milk products having a reduced lactosecontent further include other components for use in food applications,such as minerals, vitamins, non-protein nitrogen compounds, mammalianmetabolites, and combinations thereof.

Feed Stocks

Feed stocks including higher protein concentrations can also be preparedusing the processes as described herein. Particularly, by removing thelactose and other undesirable components, a concentrated feed stockincluding from about 0.5% to about 50% protein on a dry weight basis canbe prepared. Exemplary concentrated feed stocks are shown in the Tablebelow.

TABLE Exemplary Feed Stocks Lactose Solids Operational Concentrated FeedStocks content, % Range, % Whole Milk 18.75 45 to 50 Skim Milk 21.47 38to 42 Whey 24.42 30 to 34 Whey permeate 25.19 28 to 32

These feed stocks may then be used to provide concentrated sources ofprotein, lactose, and other dairy minerals in various foods such asprocess cheese, yogurt, natural cheese, ice cream, infant formulas, andanimal feed.

The disclosure will be more fully understood upon consideration of thefollowing non-limiting Examples.

Example 1

In this Example, dried milk products including lactose crystals wereprepared using the processes of the present disclosure.

Initially, skim milk powder was reconstituted with water under atemperature of from about 4° C. to about 7° C. for a period of 24 hoursto form a solution having approximately 40% by weight total solids. Thesolution was tempered at room temperature and remained at roomtemperature for a period of about 4 hours. The solution was thenpasteurized at a temperature of about 71° C. for a period of about 30minutes. The pasteurized solution was then seeded with lactose crystals,agitated, and cooled to a temperature of about 12° C. to begincrystallization. Crystallization took place during the next 48 hours ata temperature of less than 10° C. and a cooling rate of approximately0.2° C. to 0.4° C. per hour with agitation of about 50 rpm. Once thelactose had crystallized, the solution was spray dried using a spraydryer with an air inlet temperature ranging from 150° C. to 220° C. toproduce a dried milk product.

The dried milk product was analyzed, and it was confirmed that lactosein the form of α-monohydrate crystals having an average particle size of93±46 μm had formed in the dried milk products.

Example 2

In this Example, dried milk products produced in Example 1 were analyzedprior to and after separation of the lactose crystals using an airclassifier. The dried milk products produced in Example 1 and theresulting dried protein fortified milk products having reduced lactosecontent obtained after treatment with an air classifier were thencompared to control samples of skim milk powder produced fromreconstituted powdered milk.

Specifically, the dried milk products of Example 1 and control sampleswere analyzed for particle size distribution and chemical analysis priorto air classification. The results are shown in FIGS. 4A-4B. Both thedried milk products (i.e., test samples) and control samples were thentreated with an air classifier, commercially available from RSG, Inc.(Sylacauga, Ala.). Two different cut size ratios, 50:50 and 60:40, wereused for the test samples and control samples. Further the fine stream(i.e., stream without large lactose crystals) and coarse stream (i.e.,stream including high content of lactose crystals) produced by the airclassifier from both the test samples and control samples were analyzedfor concentration of protein, ash, moisture and lactose. The results areshown in the Table below.

TABLE Mass % % % Lactose % by (g) % Coding Protein Ash Moisturedifference* Test Sample 50:50 Fines 47 52.40 Fines #1 36.8 8.12 4.9 50.2Coarse 42.7 47.60 Coarse #1 34 7.58 4.9 53.5 Total Mass, g 89.7 100.00 —— — — — Test Sample 60:40 Fines 66.2 67.28 Fines #2 36.1 8.03 4.9 51.0Coarse 32.2 32.72 Coarse #2 34.1 7.6 4.9 53.4 Total Mass, g 98.4 100.00— — — — — Control Sample 50:50 Fines 76.5 52.76 Fines #3 34.7 7.73 3.753.8 Coarse 68.5 47.24 Coarse #3 34.2 7.71 3.7 54.4 Total Mass, g 145100.00 — — — — — Control Sample 60:40 Fines 58.4 60.08 Fines #4 34.77.72 3.7 53.9 Coarse 38.8 39.92 Coarse #4 34.6 7.6 3.7 54.1 Total Mass,g 97.2 100.00 — — — — — *Percentage of lactose was calculated bysubtracting from 100% the sum of protein %, moisture %, fat %, and ash %of the samples. For the fat %, it is assumed to be 0 as the samples arederived from skim milk products.

As shown in the Table above, increased amounts of lactose were removedfrom the test samples using the air classifier as compared to thecontrol sample.

Additionally, particle size distribution and chemical analysis of thefine and course streams post air classification were also analyzed forthe test samples and control samples. The results are shown in FIGS.5A-5F.

Example 3

In this Example, dried skim milk products were prepared and analyzed forthe development and morphology of α-monohydrate crystals in theproducts.

α-lactose monohydrate crystals were formed in concentrated skim milk atapproximately 40% by weight total solids. This crystallization intendedto grow lactose crystals greater than 30 μm by the following series ofconditions: 1) reconstitution of skim milk powder (commerciallyavailable from Dairy America, Fresno, Calif.), 2) batch pasteurization,3) crystallization of lactose in concentrated product, and 4)measurement of lactose crystals in concentrated product.

The concentrated skim milk was prepared from reconstitution of skim milkpowder in deionized water, allowed to hydrate for no less than 24 hoursunder refrigeration conditions. After hydration, concentrated skim milk(total solids content of approximately 40% by weight) was tempered atroom temperature for no less than 4 hours, followed by pasteurization at71° C. for 30 min. After pasteurization, the concentrated skim milk wascooled to 12° C. and then seeded with lactose powder at 0.005, 0.0075 or0.010 percent w/w. Seeding was required due to the low supersaturationlevel of lactose at 26.2 percent in water at 20° C. This calculatedvalue exceeded the lactose supersaturation threshold of 18% in water at20° C. and it is located within the lower metastable zone shown in FIG.6. The lower metastable zone requires the presence of lactose seeds topromote crystallization within a short period of time. The lowermetastable zone also enhances secondary nucleation of lactose from finecrystals. Secondary nucleation results from certain conditions ofconcentration, temperature and nuclei generated from the contact betweencrystals, crystallizer walls or stirrer.

Seed size was selected by using commercial lactose powder (availablefrom Leprino Foods, Denver, Colo.) of commercial size designation at 40,100 or 200 mesh. Following the concentrated skim milk-lactose seeding,140 g of sample material was transferred to a 150 ml temperatureprogrammable reactor to initiate crystallization. Duringcrystallization, the sample material was cooled at a rate of 0.2, 0.3 or0.4° C. per hour and agitated with a speed of 50, 70 or 100 rpm.Agitation was performed with a Caframo anchor paddle as illustrated inFIG. 3A. An alternative paddle for use with the processes of the presentdisclosure is illustrated in FIG. 3B. Final temperature after coolingwas selected at 5, 7 or 10° C., which was also the final holdingtemperature once cooled from 12° C. The cooling rate of 0.4° C. per hourwas used when the final temperature of 5° C. was selected and thecooling rate of 0.3 or 0.2° C. per hour was used when the finaltemperature of 7 or 10° C. was selected, respectively. FIG. 7 shows thecrystallization cooling profiles. Concentrated skim milk withcrystallized lactose was sampled for photomicrographs at 24 and 48 hours(FIGS. 8A-8B).

Control sample was prepared from reconstitution of skim milk powder inwater and allowed to hydrate for not less than 24 hours underrefrigeration conditions. After hydration, 27 kg of control concentratedskim milk (approximately 40% by weight total solids) was tempered atroom temperature for not less than 4 hours, followed by pasteurizationat 71° C. for 30 min. After pasteurization, control concentrated skimmilk was stored under refrigeration conditions for not less than 12hours before drying. After refrigerated storage, control concentratedskim milk was thermally treated at 50° C. for not less than 15 minutes.This thermal treatment intended to dissolve any crystallized lactose asa result of storage under refrigeration conditions. Following thermaltreatment, the control concentrated skim milk was dried in an APV pilotspray drier type PSD55 (available from Aron Equipment Company,Bensenville, Ill.). Collected control sample was sent for airclassification through contract services of RSG Inc. (Sylacauga, Ala.).In addition, control sample was fractionated by using sieves of U.S.Standard number 120, 140, 200, and 270, as well as collection pan.

Applied experimental design model for development and morphology ofα-lactose monohydrate crystals in a wet solution used a replicatedtwo-level, four factor full factorial design. Factor levels used werecrystallization temperature (5 and 10° C.), lactose seedingconcentration (0.005 and 0.010% w/w), lactose seed size (200 and 40mesh), and agitation speed (50 and 100 RPM). The factorial designexperimental model is shown in the Table below. Replication of runsfacilitated the estimation of variation between runs executed undersimilar experimental conditions. Additional center points were added tothe design intended to determine linearity or curvature of the model.Considered center points included crystallization temperature at 7° C.,lactose seeding concentration at 0.0075% w/w, lactose seed size at 100mesh and agitation speed at 70 RPM. Analysis of data from thisexperimental design model was performed by regression with the aid ofMinitab® 16.2.0 (Microsoft 2010).

TABLE A 2⁴ Factorial design experiment to study the effect from factorsA, B, C, and D in crystallization and growth of lactose crystals greaterthan 30 μm in concentrated skim milk at approximately 40% by weighttotal solids Levels Code Factors − + A Lactose Seeding 0.0050 0.010Concentration, % B Crystallization 5 10 Temperature, ° C. C Lactose SeedSize 40 200 D Agitation Speed, 50 100 RPM Standard Center Factors OrderPoints Blocks A B C D Sample Number 1 R1 1 2 0.0050 5 40 50 2 RI 1 10.0100 5 40 50 3 RII 1 1 0.0050 10 40 50 4 R4 1 2 0.0100 10 40 50 RunNumber 5 RIII 1 1 0.0050 5 200 50 6 R6 1 2 0.0100 5 200 50 7 R7 1 20.0050 10 200 50 8 RIV 1 1 0.0100 10 200 50 9 RV 1 1 0.0050 5 40 100 10R2 1 2 0.0100 5 40 100 11 R3 1 2 0.0050 10 40 100 12 RVI 1 1 0.0100 1040 100 13 R5 1 2 0.0050 5 200 100 14 RVII 1 1 0.0100 5 200 100 15 RVIII1 1 0.0050 10 200 100 16 R8 1 2 0.0100 10 200 100 17 R1 1 3 0.0050 5 4050 18 RI 1 3 0.0100 5 40 50 19 RII 1 3 0.0050 10 40 50 20 R4 1 3 0.010010 40 50 21 RIII 1 3 0.0050 5 200 50 22 R6 1 3 0.0100 5 200 50 23 R7 1 30.0050 10 200 50 24 RIV 1 3 0.0100 10 200 50 25 RV 1 3 0.0050 5 40 10026 R2 1 3 0.0100 5 40 100 27 R3 1 3 0.0050 10 40 100 28 RVI 1 3 0.010010 40 100 29 R5 1 3 0.0050 5 200 100 30 RVII 1 3 0.0100 5 200 100 31RVIII 1 3 0.0050 10 200 100 32 R8 1 3 0.0100 10 200 100 33 CP1 0 10.0075 7 100 70 34 CP2 0 1 0.0075 7 100 70 35 CP3 0 2 0.0075 7 100 70 36CP4 0 2 0.0075 7 100 70 37 CP5 0 3 0.0075 7 100 70 38 CP6 0 3 0.0075 7100 70Interpretation of the above columns is as follows: Center point 1represents the configuration of the factors at their highest or lowestlevels. Center point 0 represents the configuration of the factorsbetween their highest and lowest levels. Block 2 represents the firstexperimental runs. Block 1 represents the second experimental runs, andBlock 3 represents the third experimental runs.

Analyzed photomicrographs (FIGS. 8A-8B) from all treatments ofcrystallized lactose in the concentrated skim milk samples had anaverage mean crystal size distribution and standard deviation of 74±36nm at 24 hour and 89±44 nm at 48 hour crystallization. The largestandard deviation from these crystal size distributions at 24 and 48hours was attributed to the secondary nucleation of lactose crystalsfrom contact nucleis. Contact nuclei were generated as a result ofcrystals colliding with each other, with the walls of the crystallizeror with the stirrer during crystallization.

Factorial design analysis of 24 and 48 hour concentrated skimmilk-lactose crystallized samples revealed a significant effect fromlactose seed size only during 24 hour crystallization (FIG. 9).Increasing lactose seed size level from 40 to 200 mesh caused an averageresponse increase of 4 μm (P=0.031, α=0.050). This average responseincrease was attributed to the lower secondary nucleation of lactosefrom seeded concentrated skim milk with 200 mesh lactose powder. Thegreater number of lactose seeds from 200 mesh lactose powder provided alarger number of nuclei for crystallization, as compared to 40 meshlactose powder (see Table below).

TABLE Correlation between lactose powder mesh size, size in microns,volume, mass and number of seeds per 100 g sample Lactose Number ofLactose Lactose see lactose powder seed con- Lactose seeds mesh size,centration, Lactose seed seed mass, per 100 g size μm % volume, mm³ mgsample 200 74 0.010 9.0185 × 10⁻⁵ 1.39 × 10⁻⁴ 71,768 200 74 0.005 9.0185× 10⁻⁵ 1.39 × 10⁻⁴ 35,884 40 420 0.010  1.65 × 10⁻² 2.55 × 10⁻² 393 40420 0.005  1.65 × 10⁻² 2.55 × 10⁻² 196

This larger number of nuclei delayed crystal growth by dividing theavailable supersaturation among the nuclei. Hypothetically, this delayof crystal growth may reduce the formation of large crystals, loweringtheir probability for contact nucleation. The rate of contact nucleationalso increased with an increase in the size of the seeds. The number oflactose seeds was calculated by assuming an average seed size of 74 μmfor 200 mesh lactose powder and 420 μm for 40 mesh lactose powder.Conversion of mesh size to microns was performed by using a particlesize conversion table from Sigma-Aldrich Co. LLC (2011). In addition tothese assumptions, Equation A and Equation B were also used as well as aspecific gravity of 1.545 for α-lactose monohydrate.

V=(πD ³)/6,mm ³ D ³ =L/1.33  Equation A: Lactose seed volume

where V represents the volume of a lactose seed crystal (mm³) and Drepresents the diameter of a lactose crystal (μm³). D assumes aspherical shape for a lactose crystal, and it is determined by measuringthe length from the longest edge of a lactose crystal, which is alsodivided by 1.33. The longest edge of a lactose crystal is represented byL, (μm).

Number of lactose seeds=((% lactose seed crystals×concentrated skim milksample)×1000))/(Mass of the Crystal)  Equation B: Number of lactoseseeds

Factorial design analysis of 48 hour crystallization revealed asignificant effect from crystallization temperature. In addition to thesignificance from crystallization temperature, a marginally significantthree-factor interaction was seen between lactose seed concentration,lactose seed size, and agitation speed (FIG. 10). Increasingcrystallization temperature level from 5 to 10° C. caused an averageresponse increase of 4 μm (P=0.030, α=0.05). This average responseincrease was attributed to a lower secondary nucleation of lactosecrystals from the crystallization temperature at 10° C. This lowersecondary nucleation may relate to the lower rate of crystals growth,which may reduce the probability of contact nucleation. Conversely,crystallization temperature at 5° C. may increase the rate of crystalgrowth, which increases as the temperature decreased from the solubilitypoint. The increase on the rate of crystal growth from crystallizationtemperature at 5° C. may enhance the probability of contact nucleigeneration, promoting secondary nucleation.

The three-factor interaction between lactose seed concentration, lactoseseed size, and agitation speed caused an average response decrease of 3μm (P=0.045, α=0.05). Interpretation of this three-factor interaction islimited due to its marginal significance on the experimental model andit could be attributed to the aggregate experimental error. Responsesurface analysis was performed at 24 and 48 hour crystallization.Results from these analyses reflected no significant contribution of thecenter points at these crystallization time periods, therefore theresults are not shown.

Verification of factorial design and response surface analyses for 24and 48 hour concentrated skim milk-lactose crystallized samples wereperformed by an analysis of variance. This analysis confirmed thesignificant effect contribution of lactose seed size during 24 hourcrystallization (P=0.031; α=0.05). It also reflected that during 24 hourcrystallization the present experimental model is significantly affectedby Blocking (P=0.004; α=0.05) (see Table below).

TABLE Summary of significant effects, coefficients and analysis ofvariance for 24 hour crystallization response, μm Estimated effects andcoefficients for 24 hour crystallization response, μm Significant Coef-estimated Term Effect ficient Coefficient t P Lactose seeding 4 1.7720.7605 2.33 0.031 concentration, % Analysis of Variance for 24 hourcrystallization response, μm Source DF Seq SS Adj SS Adj MS F P Blocks 2272.286 271.703 135.851 7.34 0.004 Lactose seeding 1 98.506 100.501100.501 5.43 0.031 concentration, %

Blocking was performed as a function of time, where experimental runsfor Block 2 were performed three months prior to experimental runs forBlock 1. This significant effect from blocking is attributed to datavariability between runs. Analysis of variance during 48 hourcrystallization confirmed the significant effect contribution ofcrystallization temperature (P=0.030; α=0.05) andthree-factor-interaction between lactose seed concentration, lactoseseed size, as well as agitation speed (P=0.045; α=0.05). This analysisalso confirmed the second-order response model for 48 hourcrystallization (P=0.030; α=0.05), which was attributed to experimentalerror (see Table below).

TABLE Summary of significant estimated effects, coefficients andanalysis of variance for 48 hour crystallization response, μm Estimatedeffects and coefficients for 48 hour crystallization response, μmSignificant Coef- estimated Term Effect ficient Coefficient t PCrystallization 4 1.905 0.8116 2.35 0.030 temperature, ° C. Lactoseseeding −3 −1.743 0.8116 −2.75 0.045 concentration, %/Lactose seed size,mesh/ agitation speed, RPM Analysis of Variance for 24 hourcrystallization response, μm Source DF Seq SS Adj SS Adj MS F PCrystallization 1 134.85 116.091 116.091 5.51 0.030 temperature, ° C.Lactose seeding 1 97.27 97.266 97.266 4.61 0.045 concentration,%/Lactose seed size, mesh/ agitation speed, RPM Curvature 1 116.59116.594 116.591 5.53 0.030

Example 4

In this Example, dried skim milk products prepared similar to theproducts in Example 3 were analyzed after separation of the lactosecrystals using an air classifier.

The dried skim milk product sample (also referred to herein as testsample) was prepared from reconstitution of skim milk powder(commercially available from Dairy America, Fresno, Calif.) in deionizedwater and allowed to hydrate for no less than 24 hours underrefrigeration conditions. After hydration, 27 kg of concentrated skimmilk (approximately 40% by weight total solids) was tempered at roomtemperature for no less than 4 hours, followed by pasteurization at 71°C. for 30 min. After pasteurization, concentrated skim milk was cooledto 12° C. and then seeded with lactose powder at 0.005 percent w/w. Seedsize was selected by using commercial lactose powder (available fromLeprino Foods, Denver, Colo.) of commercial size designation at 200mesh. Following concentrated skim milk-lactose seeding, the product wastransferred to a 57 kg jacketed tank equipped with a modified agitator.This modified agitator reassembled the Caframo anchor shape paddledesign and obtained a similar crystal size distribution as the one usedin Example 3. The agitator had no contact with the sides of the vessel,thereby preventing shattering of the crystals by mechanical touching.During crystallization, the product was cooled at a rate of 0.4° C. perhour and agitated at 5 RPM. Final temperature after cooling was selectedat 5° C., which was also the final holding temperature once cooled from12° C. Following crystallization, the concentrated skim milk was driedin an APV pilot spray drier type PSD55. Collected dried skim milkproduct was sent for air classification through contract services of RSGInc. (Sylacauga, Ala.). In addition, dried skim milk product wasfractionated by using sieves of U.S. Standard number 120, 140, 200, and270, as well as collection pan. Two test runs were performed toguarantee reliable statistical analysis. This fractionation technologywas also applied to a control sample.

Applied experimental design model for analyzing the control sample andtest sample by lactose crystallization, drying, and air classificationused a two-sample t-test comparison with α=0.05. This two-sample designused protein content of control sample and test sample as comparativevariables. Experimental design for protein content of air classifiedstreams and sieved fractionated test sample was also compared by atwo-sample t-test comparison with α=0.05.

Protein content was analyzed by the Kjeldahl method with 6.38 N asprotein factor. This assay is in accordance with the modified versionsof standard methods 955.04 and 979.09 from the AOAC INTERNATIONAL, 18thEd. Ash content was analyzed with a modified version of the standardmethod 923.03 from the AOAC INTERNATIONAL, 18th Ed. Moisture content wasanalyzed with a modified version of standard method 15.111 from StandardMethods for the Examination of Dairy Products (Wehr, H. M. and Frank, J.F. 2004). Lactose content was determined by difference from the sum ofthe percentages of protein, moisture, ash and fat. Fat content wasassumed to be 0.05 percent. Microbiological analysis by petrifilmaerobic plate count was done to monitor the absence of microbiologicalinfluence on the system.

Chemical analysis of test sample fine stream reflected a protein contentsignificantly greater than the control sample fine stream (P=0.031;α=0.05). The average protein content of test sample fine stream was36.2% w/w and 35.6% w/w for control fine stream (see Table below).

TABLE Average chemical composition of air classified streams after 50:50cut size Product Fine Stream Coarse Stream Description Protein, %Lactose, % Protein, % Lactose, % Control 35.6 + 0.14 54.8 + 2.62 35.4 +0.21 53.3 + 0.11 Sample Test Sample 36.2 + 0.23 51.9 + 1.07 34.6 + 0.0653.9 + 0.72This greater protein content from test sample fine stream was attributedto the presence of crystallized lactose in the feed stock. Crystallizedlactose contributed to the displacement of coarse particles by means ofair classification. Air classification used physical forces such ascentrifugal, collision and aerodynamic drag to take advantage of theshape and size of the crystals.

Further protein fortification could be obtained in the test sample finestream than the currently gained. Two-sample t-test comparisons of meancrystal size distributions prior- (102±43 μm) and post-heating (91±39μm) reported a significant reduction of mean crystal size distributionpost-heating (P=0.000; α=0.05). This significant reduction of meancrystal size distribution from post-heated lactose crystallizedconcentrated skim milk or spray drier feed material was attributed to anincrease of the lactose solubility. The increase of the lactosesolubility related to heating of feed material with a temperature rangeof 21 to 32° C. and held for approximately 10 min. Heating was performedwith the intent to overcome the limiting processing capacities from theAPV PSD55 drier, which was not capable of operating with a feed materialat 5° C. and with an approximated 40% by weight total solids. Thisoperational drawback could be prevented by increasing the processingcapacity of the drier, or by employing a spinning-disk atomizer, or bythe combination of both. A greater processing capacity of the drier canextend the residence of the droplets in the drying chamber, consequentlycompensating for their low rate of evaporation. The low rate ofevaporation of the droplets is correlated to their total solids content,feed temperature and size.

The elevated total solids content of the droplets reduced theirconvective heat transfer with the drying medium, obscuring their waterdiffusion. Water diffusion is also affected by temperature of the feedmaterial, which affects the amount of energy required to evaporate thewater from the droplets. An additional factor influencing the rate ofevaporation is the size of the droplets. The size of the droplets iscorrelated to their surface to mass ratio, and this can improve thewater diffusion with the exhaust air by increasing the surface to massratio. This increase on surface to mass ratio improves the dryingcapacity of the droplets and reduces the amount of energy required. Thesize of the droplets can be controlled by the peripheral speed of aspinning-disk atomizer or by the degree of atomization from theswirl-type pressure nozzle. The flexibility of the spinning-diskatomizer makes it ideal for this type of application in which the feedmaterial has high total solids and crystallized lactose.

Measurements of particle size distributions by laser scattering using aMalvern 2000 (available from Malvern Instruments, Worcestershire, UK) offeed stocks from powdered control and test sample prior to airclassification reflected a D_([4,3]) of 56.08 μm for the former and58.86 μm for the latter. Two outcome streams resulted from the airclassification of these feed stocks with a 50:50 cut size (see Table;FIG. 11). First outcome, fine stream with a D_([4,3]) of 41.30 μm forcontrol sample and 44.96 μm for test sample. Second outcome, coarsestream with a D_([4,3]) of 85.58 μm for control sample and 85.92 μm fortest sample.

TABLE Average particle size distributions of feed stock, fine stream andcoarse stream of control sample and test sample D_([4,3]), D(0.1),D(0.5), D(0.9), Sample Description μm μm μm μm Uniformity Control FeedStock 56.08 11.52 46.19 112.60 0.6924 Control Fine Stream 41.30 9.5034.76 82.88 0.6588 Control Coarse 85.58 26.16 74.90 157.88 0.5394 StreamTest Sample Feed 58.86 14.82 51.32 112.04 0.5924 Stock Test Sample Fine44.96 12.16 39.90 85.10 0.5664 Stream Test Sample Coarse 85.92 34.6278.16 149.24 0.4552 Stream Test Sample 53.42 16.94 48.98 95.66 0.49Second-Cut Stream

FIG. 11 depicts apparent bypass of particles, which refers to the amountof particles that bypasses the cut size, from the fine stream into thecoarse stream. The effect of apparent bypass on the coarse particle sizedistribution can be reduced by performing a second separation of thecoarse stream. Measurement of particle size distribution by laserscattering of second separation or second-cut test sample fine streamwith a 60:40 cut size (60% coarse and 40% fine streams) reflected aD_([4,3]) of 53.42 μm. In addition, second-cut test sample fine streamhad a mean protein content of 35.3% w/w, which was not significantlygreater than the mean protein content from control sample (P=0.880;α=0.05). These results reflected that 60:40 second-cut was not able tofurther increase the protein content from second-cut test sample finestream.

The protein content from air classified streams versus protein contentfrom sieve fractionated test sample was analyzed. Results from thisanalysis reflected a difference among protein contents at a 0.05 levelof significance. This significant difference was attributed to lowerprotein content from the air classified coarse stream as compared to theprotein content from sieve fractionated streams. This finding reflectedthat air classification, in contrast to sieve fractionation, is capableof separating fine particles with increased protein, and allocating themin the air classified fine stream. In addition to this analysis, theprotein content from sieve fractionated streams versus the proteincontent from air classified fine streams was analyzed. Results from thisanalysis did not have enough evidence to conclude a significantdifference. Furthermore, protein content between sieves did not haveenough evidence to conclude a significant difference at 0.05 significantlevel.

Example 5

In this Example, dried skim milk concentrates were prepared and seededwith lactose. The lactose crystals produced therefrom were analyzed.

The dried skim milk concentrate was prepared by placing a skim milkconcentrate into a rotary evaporator for a sufficient period for theconcentrate to reach approximately 40% by weight total solids. Dissolvedsugar, expressed in ° Brix was measured using a hand-held refractometerand the sugar content was adjusted by adding distillated deionized waterto the concentrate. The evaporated skim milk concentrate was conditionedin a 250-mL beaker cooled to 12° C. and then seeded with 200 meshα-lactose monohydrate crystals at a 0.010% w/w concentration. Duringcrystallization, the sample material was cooled at a rate ofapproximately 0.4° C. per hour and agitated at a speed of 20 RPM using aU-shaped agitator similar to that used in Example 3. This preparationmethod was replicated four times, producing four samples of skim milkconcentrate.

Skim milk concentrate with crystallized lactose was sampled forphotomicrographs at 24 hours. Cystallographic analysis of the lactosecrystals was conducted by analyzing photomicrographs taken using a Nikon2 mp digital camera with support software, NIS Elements F Package, andevaluated with Image J 1.44i software. The results are shown in FIG. 12.

As shown in FIG. 12, the mean crystal size from samples 1-4 ranged from62.2040 to 75.6518 μm, with a standard deviation of approximately47.0473 μm. These results demonstrate a consistency in the performedlactose crystallization process under the stipulated conditions.

What is claimed is:
 1. A process for preparing a dried protein fortifiedmilk product having reduced lactose content, the process comprising:reconstituting skim milk powder with water to produce a solution withabout 40% solids by weight; pasteurizing the solution; cooling thepasteurized solution; crystallizing lactose in the cooled solution;spray drying the solution comprising the lactose crystals to produce adried milk product; and separating the lactose crystals from the driedmilk product to form a dried protein fortified milk product.
 2. Theprocess as set forth in claim 1 wherein the skim milk powder isreconstituted with water having a temperature ranging from about 0° C.to about 7° C. for a period of from about 12 hours to about 24 hours. 3.The process as set forth in claim 1 wherein the solution is pasteurizedat a temperature of from 66° C. to about 150° C. for a period of fromabout 5 seconds to about 30 minutes.
 4. The process as set forth inclaim 1 wherein the solution is pasteurized at a temperature of about71° C. for a period of about 30 minutes.
 5. The process as set forth inclaim 1 wherein the pasteurized solution is cooled to a temperature of12° C. or less.
 6. The process as set forth in claim 5 comprisingfurther cooling the cooled solution at a cooling rate of from about 0.2°C. to about 0.4° C. per hour continuously over a period of from about 12hours to about 48 hours to allow for crystallization of lactose in thecooled solution.
 7. The process as set forth in claim 6 wherein thecooled solution is further cooled to a temperature of from about 5° C.to about 10° C.
 8. The process as set forth in claim 1 furthercomprising seeding the cooled solution to crystallize lactose in thecooled solution.
 9. The process as set forth in claim 8 wherein seedingthe cooled solution comprises introducing from about 0.005% by weight toabout 0.010% by weight lactose crystals to the cooled solution.
 10. Theprocess as set forth in claim 1 wherein the solution comprising thelactose crystals is spray dried at a temperature of from about 150° C.to 220° C.
 11. The process as set forth in claim 1 wherein the lactosecrystals are separated from the dried milk product using an airclassifier.
 12. A process for preparing a dried protein fortified milkproduct having reduced lactose content, the process comprising:pasteurizing a liquid skim milk solution having a solids content ofabout 40% by weight; cooling the pasteurized solution; crystallizinglactose in the solution; spray drying the solution comprising thelactose crystals to produce a dried milk product; and separating thelactose crystals from the dried milk product to form a dried proteinfortified milk product.
 13. The process as set forth in claim 12 whereinthe solution is pasteurized at a temperature of from 66° C. to about150° C. for a period of from about 5 seconds to about 30 minutes. 14.The process as set forth in claim 12 wherein the solution is pasteurizedat a temperature of about 71° C. for a period of about 30 minutes. 15.The process as set forth in claim 12 wherein the pasteurized solution iscooled to a temperature of 12° C. or less.
 16. The process as set forthin claim 15 comprising further cooling the cooled solution at a coolingrate of from about 0.2° C. to about 0.4° C. per hour continuously over aperiod of from about 12 hours to about 48 hours to allow forcrystallization of lactose in the cooled solution.
 17. The process asset forth in claim 16 wherein the cooled solution is further cooled to atemperature of from about 5° C. to about 10° C.
 18. The process as setforth in claim 12 further comprising seeding the cooled solution tocrystallize lactose in the cooled solution.
 19. The process as set forthin claim 18 wherein seeding the cooled solution comprises introducingfrom about 0.005% by weight to about 0.010% by weight lactose crystalsto the cooled solution.
 20. The process as set forth in claim 12 whereinthe solution comprising the lactose crystals is spray dried at atemperature of from about 150° C. to 220° C.
 21. The process as setforth in claim 12 wherein the lactose crystals are separated from thedried milk product using an air classifier.
 22. A dried proteinfortified milk product having reduced lactose content, the dried proteinfortified milk product prepared by a process comprising: pasteurizing askim milk solution having a solids content of about 40% by weight;cooling the pasteurized solution; crystallizing lactose in the solution;spray drying the solution comprising the lactose crystals to produce thedried milk product; and separating the lactose crystals from the driedmilk product to form the dried protein fortified milk product.
 23. Thedried protein fortified milk product as set forth in claim 22 comprisinga protein content of from about 38% by weight to about 56% by weight.24. The dried protein fortified milk product as set forth in claim 22comprising a lactose content of from about 35% by weight to about 52% byweight.
 25. The dried protein fortified milk product as set forth inclaim 22 further comprising at least one of minerals, vitamins,non-protein nitrogen compounds, and mammalian metabolites.
 26. The driedprotein fortified milk product as set forth in claim 22 comprising lessthan 5% by weight moisture.